This article discusses the basic findings that enable a determination of the thicknesses of the adsorbed water layers on the external surfaces of clay minerals and their dependence on the total water content in soils. The thicknesses of the water films were first determined indirectly from tests of the undrained shear strength of clay mineral samples. A comparison between these thicknesses and the total quantity of water in the samples showed that this ratio is exactly defined and can be expressed by a non-linear function in which the type of soil is determined by two parameters, which depend on the size and the quantity of the clay minerals. A test of the correctness and usefulness of the established expression was made on two samples of clays. The thicknesses of the water films, calculated using the proposed equation for different moisture contents, were compared with the thicknesses determined from the adsorptive potential of the soils. These results showed a good agreement. The possible application of the proposed expression is shown for the case of an estimation of the soil–water characteristic curve in the range between the water content at the air-entry value and the residual water content.
COBISS.SI-ID: 19417110
The majority of slope failures are triggered by excessive rainfall and the consequent increase in pore-water pressure within the slope. This paper presents the results of a computer code that quantifies earth pressure coefficients. This code is based on limit-equilibrium analyses and is used for the internal design of geosynthetic reinforced soil structures and to identify the critical failure mechanism. The critical failure mechanism is the largest value of out-of-balance force. For this purpose, the nonlinear programing (NLP) approach was used, and a NLP optimization model, TMAX, was developed. The model was used for failure mechanisms, assuming that the failure surfaces were bilinear. The influence of pore-water pressure on the potential failure surface was analyzed. The model was developed under basic principles. Optimally, the system is best suited for structures with varying geometries, different backfill unit weights, varying types of soil shear resistance, and different pore-water pressures. A numerical example was used to demonstrate the effect of pore-water pressure on the required strength of reinforcement and on the efficiency of the introduced optimization approach.
COBISS.SI-ID: 19256342
Velenje Coal Mine (VCM) is situated on the largest Slovenian coal deposit and one of the thickest layers of coal known in the world. The lignite seam is up to 168 m thick and the VCM’s annual production is approximately 4 million tons of coal. The thickness of the seam and its relatively small lateral dimensions are advantage with respect to the concentration of large reserves, but causes problems with the efficiency of extraction of lignite, since the majority of mining operations is within the lignite seam itself. Therefore a specific and highly productive Velenje Mining Method (VMM) was established, as an extraction method of coal from thick layers. The selected longwall coal mining method with specific geometry, the increasing depth of excavations, changes in stress state and naturally given geomechanical properties of rocks induce seismic events. Induced seismic events at the VCM can thus be caused by caving processes, blasting or rockbursts. Of these, rockbursts, with accompanying sound effects and seismic waves, in addition to problems with extraction, cause fear and discontent of local residents. Factors affecting the occurrence of rockbursts are geological structure, depth and thickness of coal layer under extraction, mechanical properties of rocks and stress-strain changes caused by the VMM. Based on the literature two types of rockbursts were recognized. The first type occurs in close proximity to excavations and is a direct result of the stress redistribution caused by mining conditions. The second type are rockbursts associated with movement on major geological discontinuities and are a direct result of mining, but on a larger scale. Despite of modern technology and new study methods, rockbursts can not yet be foreseen. We wanted to determine the expected locations of rockbursts, therefore the necessary data were collected and visualization of situation was made. Collected data were of mining operations in the coal layer and properties of the coal itself, hanging wall and footwall rock properties, subsidence of the surface and lake formation and data of locations of rockbursts detected at the VCM. For visualization of the data, a statistical analysis of interpolation methods of Surfer software was made. As a result of statistical evaluation of interpolation methods, the most suitable interpolation method for the display of layers, the Kriging method was chosen. Based on the thickness of the coal seam and the depth of the samples taken from the boreholes, 5 layers of the coal seam were separated. For each of the 5 layers, ash content and calorific value were determined. For 2.5D visualization of rockbursts locations in the VCM software packages Surfer12 and Voxler3 software were used.
COBISS.SI-ID: 1616735
The complex hydro-geological situation, particularly in terms of groundwater, has been a constant threat to the mining carried out at the Velenje colliery since its inception. Of particular interest to the authors are the difficulties presented to the colliery by the adjacent sand aquifers, as the water pressure within these sands directly impacts mining safety, and the aquifers themselves are most directly affected by dewatering. In order to monitor water levels and estimate dewatering at the Velenje wells, multi-layered modelling using 3D Finite Difference Method (FDM) has already been carried out. However, FDM is not optimal due to its greater dependence on cell size than on water flow. In 2017 in Velenje, a series of wells will be terminated as a result of mining and mining-induced subsidence, leading to dewatering and danger of flooding. As part of a plan to address this by replacing dewatering structures, a series of drive-in filters will be implemented around the entry and exit point tunnels of a longwall face. Because FDM seems to be inadequate for purposes of optimising this process, the Finite Elements Method (FEM) was applied in this case. Based on such an application of FEM, a prediction of the optimisation of drive-in filters was carried out by the authors.
COBISS.SI-ID: 1622367
Directional surveys have been around since the beginning of drilling in the oil and gas industry. The tools have constantly been changing during the years, which cannot be said for the calculation methods. The most common directional survey calculation methods were compared in this paper. The methods were compared with the introduction of relative differences, where each or every second, every third, or every fifth survey station is taken into consideration. The results were plotted graphically over the length of the wellbore. They were also visualized. The tangential method was found to be inappropriate for its use in any circumstances. The average angle method or balance tangential method should be used for field application whereas the helical arc method is recommended for computer calculations.
COBISS.SI-ID: 1273950